This invention relates in general to respirating devices and in particular to a new and useful warning device for a respirator having a pressure gas supply.
It is absolutely necessary for the user of a protective breathing apparatus with a pressure gas supply, to know in advance whether breathing gas will be supplied at all, and to be warned in time if the pressure gas supply is exhausted.
Prior art warning devices may signal either a residual pressure or the fact that the cylinder valve is not open or that the cylinder is empty.
A known warning device for protective breathing apparatus with pressure gas supply uses a combination of these two possibilities and provides a whistle as the signalling element which, upon opening the shut-off valve of the pressure gas supply, produces a short whistle as a checking signal indicating the readiness of the warning device, and then is actuated again for short periods of time to indicate that the pressure in the pressure gas tank dropped below a predetermined value and the gas is going to be exhausted.
This prior art warning device comprises a first pressure controlled diaphragm valve which is controlled to close under high pressure, and to open under a medium pressure and a spring force. As the high pressure drops below a desired threshold value, the open forces prevail and the first diaphragm valve opens. This enables the medium pressure to reach the signalling element, through a connecting passage and a second diaphragm valve which is designed as a pressure controlled double diaphram valve, and thus to produce the warning signal.
To minimize the pressure gas consumption, the warning time period is limited by the second diaphragm valve. In its normal position, the second diaphragm valve is open under the action of a spring. Its control members are two diaphragms and a valve-closing body secured thereto. One diaghragm has a smaller surface area and is exposed to the pressure in the connecting passage, while the other diaphragm, having a larger surface area, forms a boundary of a completely enclosed space and is exposed to the pressure which is produced in this space by the gas penetrating therein through a bore and a throttle in the valve body.
Due to the unequal surface areas of the diaphragms, the second diaphragm valve closes as the closing pressure is reached and shuts off the gas stream to the signalling element. What is disadvantageous in this warning device is the absence of a warning signal if the gas cylinder is not open or entirely empty, and a certain gas loss caused by the warning signal if the pressure drops below the threshold value (German Pat. No. 21, 29, 529).